One system to control an engine during a condition of valve actuator failure is described in U.S. Pat. No. 6,278,932. The system description presents a way to deactivate a bank of cylinders in response to a valve actuator failure. In addition, an actuator controller is provided for each bank of the engine and each controller is configured to operate valves, fuel injection, and ignition if communication between the actuator controller and engine controller is disrupted.
The above-mentioned method can also have several disadvantages. Namely, the method can cause the engine cylinders to combust air-fuel mixtures at uneven intervals between combustion events since the system deactivates an entire cylinder bank if a valve failure is detected. That is, over the course of an engine cycle (720 crankshaft angle degrees of rotation for a four-stroke engine) a first cylinder will fire (combust) followed by a first crankshaft interval, followed by a second combustion event, followed by a second crankshaft interval, followed by a second firing of the first cylinder in a second engine cycle, for example. The combustion is uneven because the first crankshaft interval distance is different than the second crankshaft interval distance. Uneven cylinder firing can cause engine noise and vibration to increase. Furthermore, continued operation of the engine in this mode may lead to further engine degradation because of the uneven torque production and engine vibration.
Another disadvantage of the before-mentioned system is that there does not appear to be a specific way to operate the engine if operation of one of the actuator controllers degrades or is deactivated. One possible action to mitigate degradation of an actuator controller is to use the same approach as when a valve actuator failure is detected, namely, to deactivate a complete cylinder bank. However, deactivating a complete cylinder bank in response to controller degradation may lead to the issues that are described above and is therefore an undesirable outcome.
The inventor herein has recognized the above-mentioned disadvantages and has developed a system that improves engine operation during degradation or deactivation of an engine controller that offers substantial improvements.